Wax coating composition and paperboard coated therewith



United States Patent WAX COATING COMPOSITION AND PAPER- BOARD COATEDTHEREWITH Eugene A. Jakaitis, Morton, Pa., assignor to The AtlanticRefining Company, Philadelphia, Pa., a corporation of Pennsylvania NoDrawing. Filed Oct. 7,1959, Ser. No. 844,864

7 Claims. (Cl. 106-270) such materials. Such wax coated paperboard isparticularly useful in the manufacture of food cartons and milkcontainers. Since parafiin wax lacks the tensile strength andflexibility characteristics required for a paperboard coatingcomposition, polyethylene in small amounts has been added to the wax toimprove these properties. The waxes suitable for coating milk cartons,however, require additional properties in order that they will coat thecar-ton uniformly and the finished cartons will have a long shelf lifewhen filled with milk. It has been found that if thicker wax coatingsare applied, longer shelf lives can be obtained, such coatings, however,are usually not uniform and tend to flake from the paperboard. Thistendency increases as the load of wax on the paperboard increases and,in addition, the material cost of waxing the paperboard increases as thewax load increases.

A wax composition now has been found wherein a paraffin wax-polyethylenecomposition is modified by the addition of small amounts of amicrocrystalline wax and a high melting point synthetic Fischer-Tropschwax to produce a wax composition which, when utilized to coatpaperboard, provides superior performance characteristies at low waxloads.

It is an object therefore of this invention to provide an improved waxcoating composition.

It is another object of this invention to provide paperboard coated withan improved wax coating composition.

It is another object of this invention to provide a wax coatingcomposition possessing superior performance characteristics at low loadlevels.

Other objects of this invention will be apparent from the followingdescription of the invention and the claims.

In accordance with the present invention, a wax composition comprising amajor amount of paraffin wax modified by the addition of small amountsof polyethylene, a microcrystalline wax, and a high melting pointsynthetic Fischer-Tropsch wax may be utilized at low wax loads to coatpaperboard, particularly milk cartons, to provide a uniformly coatedcarton having an exceedingly long shelf life.

The major componentof the wax composition of the instant inventioncomprises parafiin wax, i.e., the normal and isoparaffin hydrocarbonwaxes derived from pctroleum crude oils melting within the range of fromabout 110 F. to about 140 F. These paraffin waxes usually predominate innormal parafiins and ordinarily consist of a mixture of hydrocarbonsdiffering only slightly in .structure and molecular weight. They areobtained from waxy lubricating oils by well-known dewaxing procedures,generally by the use of dewaxing solvents. Paraffin waxes arecharacterized by their melting points and those suitable for use in thisinvention have melting points ranging from F. to 140 F. and thosepreferred have melting points ranging from F. to F.

The second essential component of the instant wax composition comprisesa solid polymer of ethylene, in particular, polyethylene having anaverage molecular weight of between about 10,000 and 14,000 (Staudingermethod). Preferably the polyethylene should have a molecular weight ofabout 12,000. Y

The third essential component of the instant wax composition is amicrocrystalline wax, sometimes designated as amorphous or petrolatumwax, such as that prepared by the solvent dewaxing and deoiling ofMid-Continent petroleum residuum stocks. The microcrystalline waxespreferred for the wax compositions of this invention are those having amelting point within the range from F. to F., a viscosity of from 80 to90 Saybolt seconds Universal at 210 R, an oil content of not more thanabout 1.5 percent and a penetration at 77 F. of

from about 23 to 30.

The fourth essential component of the wax composition of this inventionconsists of a synthetic Fisher- Tropsch wax. Fischer-Tropsch waxes whichin recent years have become available in commercial quantities areproduced by the well-known reaction of carbon monoxide with hydrogen.The waxes so produced are characterized by the fact that they containvery high percentage of normal paraffius, generally of the order of 90percent or more. The remainder of such waxes are composed of slightlybranched chain hydrocarbons and trace amounts of unsaturated compoundsand oxygenated compounds. The synthetic Fischer-Tropsch waxes suitablefor use in the instant compositions are those of high melting pointranging from 215 F. to 230 F. and preferably from 220 F. to 225 F.

It has been found that the quantity of each component used to modify theparaffin wax is exceedingly critical in order to obtain the objectivesof the invention. Thus, the quantity of polyethylene should range from0.3 to 1.0 weight percent based on the weight of the finishedcomposition, this microcrystalline wax should range from 2.0 to 4.0weight percent based on the weight of the final composition, preferablythe microcrystalline wax should amount to about 3.0 percent, and theFischer-Tropsch wax should range from 1.0 to 2.0 weight percent based onthe weight of the final composition. Thus the paraffin wax may rangefrom 93.0 to 96.7 weight percent and preferably from 94.0 to 95.7 weightpercent.

The compositions of this invention are easily prepared. Parafiin wax ismelted and the microcrystalline wax added thereto with vigorousagitation. This mixture is then heated to a temperature of approximately240 F. and the polyethylene and the Fischer-Tropsch wax added withadditional vigorous agitation. The final coating composition may beutilized for coating paperboard at coating temperatures of preferably F.

In order to demonstrate the utility of the wax coating compositions ofthis invention as well as the criticality of each of the components andthe amounts thereof, a large number of compositions were prepared andutilized to coat milk cartons according to a standard method andthereafter the coated cartons were subjected to certain performancetests.

A Model E Pure-Pak machine which takes carton blanks, forms them intocartons, waxes the cartons, fills the cartons with milk and seals thecartons in successive steps was utilized in these tests. The paperboardutilized was milk carton stock, 0.16 inch in thickneSSQhaV ing250-second Gurley densometer porosity. The ma chine was operated in thenormal way with the coating being carried out at 170 F. except that thecartons were not .filled with milk. Thus, the. wax loads ob PatentedJan. 10, 1961 tained were solely dependent upon the wax being employed.In order to determine the amount of wax load on the cartons apredetermined number of cartons was weighed before and after waxing. Thediflference in weight was determined for the number of cartons utilizedin the test and the wax load expressed in pounds per 1000 cartons. Thus,if cartons were utilized in the test the diiference in weight before andafter waxing would be multiplied by 100 in order to obtain the wax loadin pounds per 1000 cartons.

In order to determine the uniformity of the wax coating, a waxed cartonwas filled with an aqueous solution of methylene blue, 0.1 percent byweight and the solution allowed to stand in the carton for 10 minutes atroom temperature (73 F.). The solution was then poured from the cartonand the carton opened and fiattened. Wherever the wax had failed to coatthe paper, a blue stain appeared. The total area stained was measuredwith a grid ruled in squares measuring 0.25 centimeter on each side. Thetotal area stained in terms of the number of such squares was reportedas the staining number. Thus, the higher numbers indicate pooruniformity whereas low numbers correspond to a more uniform coating.

The shelf life of the waxed cartons was measured by filling the cartonwith a 1.0 percent aqueous solution of lactic acid also containing 0.1percent methylene blue and allowing the filled cartons to stand at roomtemperature (73 F.). The cartons were inspected twice daily to note thedevelopment of leaks. The number of hours required for a leak to developwas reported as the shelf life of the carton. The methylene blue, ofcourse, facilitated the detection of the leaks. It was found that thelactic acid solution simulated aged milk and therefore correlated verywell with actual shelf life of cartons containing milk.

The parafiin wax utilized in these examples had a melting point of 124F. according to ASTM Method D-87 and an oil content of 0.8 percentaccording to ASTM Method D-721. The polyethylene employed had amolecular weight of 12,000. The microcrystalline wax had a melting point(drop) of 146 F. according to the ASTM Method D-127, an oil content of1.5 percent as measured by ASTM Method D-721, a viscosity of 87 Sayboltsecond Universal at 210 F. and a penetration at 77 F. of 26.2 asmeasuredby ASTM Method D- 1321.

The synthetic Fischer-Tropsch wax was a commercial material sold underthe trade name Parafiint and had a capillary melting ,point of 221 F., asolidification point (rotating thermometer) of from 208.4 to 215.6 F., adrop melting point of about 230 F., a penetration at 77 F. of less than1, an iodine number of from 3 to 5, an acid number of 0.0, asaponification number of 0.0, and a hydroxyl number of 0.0.

The compositions which were prepared and tested together with theresults of the performance tests carried out thereon are set forth inTable I.

It .will be seen from these data that the paraffin wax alone ggives ahigh load and short shelf life whereas if the paraffin wax is modifiedwith polyethylene the wax load is decreased to a satisfactory level, butthe shelf life is not increased to a satisfactory degree and the coatingis rather non-uniform as shown by the high staining number. Example 3shows that the composition of Example 2 may 'be improved by the additionof the Fischer-Tropsch wax as far as the uniformity is concerned, butthe load is increased. Example 4 shows that the shelf life of thecomposition of Example 2 may be improved by the addition ofmicrocrystalline wax, but the load is materially increased and thecoating again becomes rather non-uniform. Example 5 shows thenecessity-of employing all three of the paralfin wax moditiers. Thiscomposition has a low load level, is uniform and has a superior shelflife.

In order to demonstrate the criticality of employing the high meltingpoint Fischer-Tropsch wax in the composition of this invention, a highmelting point microcrystalline wax was substituted for theFischer-Tropsch wax in the composition of Example 5. Thismicrocrystalline wax was a commercial product having a melting point ofapproximately 185 F. The paraffin wax, polyethylene, and lower meltingpoint microcrystalline wax were the same as those employed in Example 5and in the same amounts. The amount of high melting pointmicrocrystalline wax employed was 1.5 percent by weight, i.e. the sameas that of the Fischer-Tropsch wax in Example 5. The results of thetests on this composition are shown under Example 6 in Table II.

In another experiment the highest melting point petroleum paraiiin waxavailable commercially, melting point 163.4 F., was substituted for theFischer-Tropsch wax of Example 5. This composition designated Example 7in Table II, employed the same paraflin wax base material, polyethyleneand microcrystalline wax of Example 5 and in the same amounts as inExample 5. Likewise the high melting point parafiin wax was used in theamount of 1.5 percent by weight, the amount of the Fischer-Tropsch waxin Example 5.

Table II Wax Load, Shelf Life, Example No. Pounds Staining Hours at For1,000 Number 73 F.

Cartons These results show that neither a high melting pointmicrocrystalline wax nor a high melting point petroleum paraflin wax canbe substituted for the Fischer-Tropsch wax of this invention.

A large series of experiments were carried out in which the molecularweight and concentration of the polyethyl one were varied and the waxload determined for each composition. From the correlation curvesobtained it was determined that in order to obtain a wax load notgreater than 32.5 pounds per 1000 cartons the average molecular weightof the polyethylene should range from 10,000 to 14,000 molecular weight(Staudinger method), preferably about 12,000, and the concentrationshould range from 0.3 to 1.0 Weight percent based on the weight of thefinal composition. The concentration ranges of the microcrystalline wax(2.0 to 4.0 weight percent, about 3.0 percent preferred) andFischer-Tropsch wax (1.0 to 2.0 weight percent) were determined fromsimilar test data.

I claim:

1. A wax coating composition for paperboard consisting essentially offrom 93.0 to 96.7 weight percent of a paraffin wax having a meltingpoint ranging from F. to -F., from 0.3 to 1.0 weight percent ofpolyethylene having an average molecular weight ranging from 10,000 .to14,000, from 2.0 to 4.0 weight percent of a microcrystalline wax havinga melting point ranging from 145 F. to 160 F., and from 1.0 to 2.0weight percent of a Fischer-Tropsch wax having a melting point rangingfrom 215 F. to 230 F.

2. A wax coating composition for paperboard consisting essentially offrom 93.0 to 96.7 weight percent of a paralfin wax having a meltingpoint ranging from 120 F. to 125 F., from 0.3 to 1.0 weight percent ofpolyethylene having an average molecular weight ranging from 10,000 to14,000, from 2.0 to 4.0 weight percent of a microcrystalline wax havinga melting point ranging from about 145 F. to 160 F., and from 1.0 to 2.0weight percent of a Fischer-Tropsch wax having a melting point rangingfrom 220 F. to 225 F.

3. A wax coating composition for paperboard consisting essentially offrom 94.0 to 95.7 weight percent of a parafiin wax having a meltingpoint ranging from 110 F. to 140 F., from 0.3 to 1.0 weight percent ofpolyethylene having an average molecular weight ranging from 10,000 to14,000, about 3.0 weight percent of a microcrystalline wax having amolecular weight ranging from 145 F. to 160 F. and from 1.0 to 2.0weight percent of a Fischer- Tropsch wax having a melting point rangingfrom 215 F. to 230 F.

4. A wax coating composition for paperboard consisting essentially of94.0 to 95 .7 weight percent of a paraffin wax having a melting pointranging from 120 F. to 125 F., from 0.3 to 1.0 weight percent ofpolyethylene having an average molecular weight ranging from 10,000 to14,000, about 3.0 percent by weight of a microcrystalline wax having amolecular weight ranging from 145 F. to 160 F. and from 1.0 to 2.0weight percent of a Fischer- 'Iropsch wax having a melting point rangingfrom 220 F. to 225 F.

5. A wax coating composition for paperboard consisting essentially of94.0 to 95.7 weight percent of a paratfin wax having a melting pointranging from 120 F. to

125 F., from 0.3 to 1.0 weight percent of polyethylene having an averagemolecular weight of about 12,000,

about 3.0 weight percent of a microcrystalline wax having a molecularweight ranging from 145 F. to 160 F.

and from 1.0 to 2.0 weight percent of a Fischer-Tropsch to 14,000, from2.0 to 4.0 weight percent of a microcrys-' talline wax having a meltingpoint ranging from 145 F. to 160 F. and from 1.0 to 2.0 weight percentof a Fischer-Tropsch wax having a melting point ranging from 215 F. to230 F.

7. Paperboard having a wax coating consisting essentially of from 93.0to 96.7 weight percent of a paraflin wax having a melting point rangingfrom F. to F., from 0.3 to 1.0 weight percent of polyethylene having anaverage molecular weight ranging from 10,000 to 14,000, from 2.0 to 4.0weight percent of a microcrystalline wax having a melting point rangingfrom about F. to F. and from 1.0 to 2.0 weight percent of a Fischer-Tropsch wax having a melting point ranging from 220 F. to 225 F.

References Cited in the file of this patent UNITED STATES PATENTS2,731,370 Tramm Ian. 17, 1956 2,733,225 Smith Jan. 31, 1956 2,773,045Simerl Dec. 4, 1956 2,810,678 Eflron Oct. 22,1957 2,816,845 Capell Dec.17, 1957 2,857,350 Thompson Oct. 21, 1958 2,867,596 Bennett Jan. 6, 1959UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No.2,967,781 January 10, 1961 Eugene A. Jakaitis that error appears in theabove numbered pat- It is h'ereby certified that the said Letters Patentshould read as ent requiring correction and corrected below.

Column 1, line 19, for "coacting" read coating column 2, line 22, for"Fisher" read Fischer column 3, line 45, for "second read Seconds1(sEAL) Attest:

DAVID L. LADD Commissioner of Patents ERNEST W. SWIDER Attesting Officer

1. A WAX COATING COMPOSITION FOR PAPERBOARD CONSISTING ESSENTIALLY OFFROM 93.0 TO 96.7 WEIGHT PERCENT OF A PARAFFIN WAX HAVING A MELTINGPOINT RANGING FROM 110*F. TO 140*F., FROM 0.3 TO 1.0 WEIGHT PERCENT OFPOLYETHLENE HAVING AN AVERAGE MOLECULAR WEIGHT RANGING FROM 10,000 TO14,000, FROM 2.0 TO 4.0 WEIGHT PERCENT OF A MICROCRYSTALLINE WAX HAVINGA MELTING POINT RANGING FROM 145*F. TO 160*F., AND FROM 1.0 TO 2.0WEIGHT PERCENT OF A FISCHER-TROPSCH WAX HAVING A MELTING POINT RANGINGFROM 215*F TO 230*F.